This invention relates to a semiconductor device.
Low-breakdown-voltage MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor) has been wildly used in a notebook computer, an AC adapter of LCD (Liquid Crystal Display), a switching power source of the server, or the like, and lower ON resistance and higher speed have been required. In the low-breakdown-voltage MOSFET, the percentage of the ON resistance depending on the channel resistance is high, and therefore, the ON resistance has been reduced by miniaturization or the like. And, along with realizing reduction of the channel resistance, reduction of drift resistance has also been taken attention to.
One example of the structure reducing the drift resistance includes so-called “Super Junction Structure” which has actual performance in high breakdown voltage and in which the pn junction structure parts are provided repeatedly in the horizontal direction in the drift layer (for example, JP-A 2006-179598 (Kokai),). Moreover, in the low breakdown voltage system, in so-called “Semi Super Junction Structure” provided with p-type pillar layer to the midstream of the depth direction of n-type drift layer, it is reported that reduction of ON resistance is realized and trade-off between breakdown voltage and ON resistance is improved.